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Re: Classic computers with more than one stack pointer, but not FORTH machines.

by John

On Fri, 21 Feb 2025 12:00:07 -0600 Paul Koning <paulkoning(a)comcast.net> wrote: > > What is the problem with ISRs running in a user stack? The ISR > > runs, exits, the stack is cut back, and net effect on the user's > > stack is zero. > > A stack access fault in user mode kills the process, in kernel mode > (certainly in an ISR) it kills the whole system. You can't leave the > integrity of the OS at the mercy of the application having a valid > stack. Additionally, the ISR could leave potentially sensitive information in user memory, depending on exactly how the stack and memory protection are implemented. Consider an architecture where the stack pointer is a normal address register (as on the -11, the 68k, etc.) and protection is on a per-page basis with no bounds checking (i.e. there's no special address space for the stack, just a particular chunk mapped into normal user memory.) It'd be trivial for a user program to sit and "scrape" the stack for stray bits left by passing ISRs - say, waiting to see if the UART service routine happens to jot down something that looks like an admin password coming off one of the terminals.

7 months, 2 weeks

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Re: Elliott Algol

by Paul McJones

> On19 Feb 2025 18:39:08 -0500, Chuck Guzis via cctalk wrote: > >>> >>>> One of most ingenious coding tricks to me was the problem of saving and >>>> restoring all registers without resorting to an exchange jump. We used >>>> that one as a test for applicants. >>> >>> Argh... I know I've seen this trick, but it's been too many years. How >>> about a hint? >> >> It uses the RJ instruction to record register content, bit-by-bit. >> Think about it--RJ is about the only instruction that can modify memory >> without fiddling with the A6 and A7 registers. >> > > Of course... I vaguely recalled there was a bit-by-bit save, but didn't > think of the RJ. Thanks. A full example of this code is in the DEBUG package of CAL SNOBOL <https://mcjones.org/CAL_SNOBOL/>, starting at label SAVEREG: Original version: https://mcjones.org/CAL_SNOBOL/UArizona/SNOBOL.MAC.html Revised version: https://mcjones.org/CAL_SNOBOL/UTexas/DEBUG.html

7 months, 2 weeks

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IBM 4506 (old message)

by Tommy Chang

I saw an email posted to the predecessor mail list asking if anyone had a picture of an IBM 4506 terminal. I was looking through the September 1973 issue Modern Data and saw an article on page 70 about the New York Times’s indexing efforts. It said that they were using IBM 4506 terminals and it has a picture of a large workroom (identified as “The Times index room”) with a bunch of terminals which I assume must be 4506’s (although the caption does not explicitly state that). The magazine is available on BitSavers. Look for the issue with file name Modern_Data_1973_07.pdf. Tommy Chang

7 months, 2 weeks

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Classic computers with more than one stack pointer, but not FORTH machines.

by ben

Did any classic computers have a subroutine call as (S++)=PC, PC=(EFA) as well as the standard call (--S)=PC,PC=(EFA) ? One could have a virtual stack machine, using helper functions without having to deal with return addresses on the stack. Ben.

7 months, 2 weeks

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Re: Classic computers with more than one stack pointer, but not FORTH machines.

by John

On Tue, 18 Feb 2025 12:00:10 -0600 cctalk-request(a)classiccmp.org wrote: > On the more than "one stack pointer" in the subject, it was a bit > arbitrary on the PDP-11 (or VAX) as the pre/post indexed indirect > addressing made every register a stack pointer. But this is where I > get hazy between DEC and 68K, and I did a lot more 68K. I'm pretty > sure you could do a move.l PC, An and you could certainly do an > indirect jmp (An), so effectively you could have multiple call stacks > if you wanted. Almost, kinda-sorta. The JSR and RTS instructions are hard-wired to use R6/SP, and there's nothing you can do about that. You *can* implement a return off another "stack" by doing e.g. MOV @(Rn)+, PC as long as you save the return address by hand, first - but this affects the flags, unlike JSR/RTS.

7 months, 2 weeks

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HAWLEY X063X Mark II and XEROX Star mice

by hupfadekroua

Hi all, I‘m offering HAWLEY X063X, XEROX Star rollerball and optical mice. If interested contact me offlist please. Best Andreas

7 months, 2 weeks

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VCF SoCal 2025 recap

by Steve Lewis

Happened to be in the area, so I checked out VCF SoCal last weekend. Glad I did, wow Lee Felsenstein was able to present ! What a treat. VCF SoCal 2025 — voidstar <https://voidstar.blog/vcf-socal-2025/> https://voidstar.blog/vcf-socal-2025/

7 months, 2 weeks

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Re: Elliott Algol

by Paul McJones

> On 15 Feb 2025 18:41:21 -0800,Van Snyder <van.snyder(a)sbcglobal.net <mailto:van.snyder@sbcglobal.net>> wrote: > > Harry Husky, the G15 designer, was one of the computer design pioneers. > He became a professor (maybe adjunct) at UC Berkeley. As far as I know, Huskey was a regular professor. Two of his Ph.D. students went on to win the ACM Turing Award: Niklaus Wirth and Butler Lampson: https://mathgenealogy.org/id.php?id=10185 Huskey went on to found the Computer Science department at U.C. Santa Cruz.

7 months, 2 weeks

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Re: Elliott Algol

by Paul McJones

> On 16 Feb 2025 18:00:35 -0700,ben <bfranchuk(a)jetnet.ab.ca <mailto:bfranchuk@jetnet.ab.ca>> wrote: > > I have trouble understanding the fine points of accessing a local > variable in Algol with a display. Books tend to spend more time > on the evils of a dangling else, and gloss over the run time action of > a display. > Have a good example or reference book I can find free on line. The original book on that subject is ALGOL 60 Implementation by B. Randell and L. J. Russell. It’s available here with permission from the copyright holder: https://www.softwarepreservation.org/projects/ALGOL/algol60impl/#ALGOL_60_I…

7 months, 2 weeks

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Open source a panacea?

by Donald Whittemore

I am an old mainframe guy. I could give you my COBOL deck of cards or the compile listing. You could pour through the code looking for nefarious/malicious code. I then hand you the object deck. You have no idea if it matches the code you looked at. The only way you could be sure is to compile the code I gave you and use your own object deck. So why is open source these days such a beneficial thing? DeepSeek may be open source but I have no way to create my own executable. Besides, I don’t know what language it is written in but I bet I have no expertise in it. No way to for me to identify nasty code. Yes, many people may have reviewed the code but that does not mean what I am running is the result of that code.

7 months, 3 weeks

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